You can pull your own hair or poke yourself and it won't
  feel much different than if someone else is doing it for
  you. But even the most ticklish among us will admit that
  tickling solo borders on the boring (please, no feedback on
  how you tickle yourself - some things really ought to
  remain private).

  Most experts agree the reason is that a tickle requires a
  combination of aggressiveness, sexuality and the element of
  surprise to induce a laugh. No matter how much you love
  yourself or how aggressive you get, you're still going to
  have a heck of a time surprising yourself.